1. Field of the Invention
The present invention relates to alarm devices, and more particularly to alarm devices adapted to indicate the unauthorized withdrawal of a plug from a wall socket.
2. Description of the prior art
With the present rise in crime, and particularly crime against property, various alarm devices for protection of property have been developed. Most such prior art alarm systems are directed at detecting unauthorized entry into a protected building and therefore entail various techniques for monitoring the places of egress and ingress. For this reason, most prior art alarm systems involve a large financial outlay and therefore have not been commonly accepted by the consumer. While such prior alarm systems do protect the whole building, very often the criminal entering the building does so for the purpose of removing conveniently portable items, such as portable appliances. Electrical appliances, in particular, typically represent a large investment to an average person and are furthermore conveniently packaged for portability and resale. Each such electrical appliance is usually connected to a wall receptacle, this connection being very rarely disrupted in normal use. The unauthorized taking of such portable appliances will therefore most often entail the withdrawal of the plug from the receptacle. Heretofore this particular feature has not been utilized to advantage in the prior art alarm systems.
In addition to the features set forth above, most present-day appliances include in their connecting interfaces, a three-terminal connection where the third terminal is normally the grounding terminal of the device. The receptacle is similarly provided with a ground contact, which, under proper circumstances, is essentially a zero potential. Any alarm mechanism utilizing this ground contact does not require any isolation or voltage protection.